JPWO2013145318A1 - Honeycomb filter and method for manufacturing honeycomb filter - Google Patents

Abstract

In the honeycomb filter of the present invention, a large number of cells for circulating a fluid are arranged in parallel in the longitudinal direction across the cell wall, and the end of either the fluid inflow side or the fluid outflow side of the cell is sealed. A ceramic honeycomb substrate including a porous honeycomb fired body, a cell wall surface of a cell in which an end portion on a fluid inflow side is opened and an end portion on a fluid outflow side is sealed, and a pore portion in the cell wall A filtration layer comprising at least two layers formed, wherein the filtration layer comprises a first layer in which particles having a first average particle diameter are deposited on a surface of the cell wall; and the first layer. A particle having a second average particle size smaller than the average particle size includes a second layer deposited on the surface of the first layer.

Description

The present invention relates to a honeycomb filter and a method for manufacturing a honeycomb filter.

The exhaust gas discharged from an internal combustion engine such as a diesel engine contains particulates such as soot (hereinafter also referred to as PM), and this PM causes a problem to the surrounding environment or the human body. ing.
Further, since the exhaust gas contains harmful gas components such as CO, HC and NOx, there is a concern about the influence of the harmful gas components on the environment or the human body.

Therefore, an exhaust gas purification device is used to collect PM in exhaust gas and purify harmful gas components.
Such an exhaust gas purification device is manufactured using a honeycomb filter made of a material such as ceramic. The exhaust gas can be purified by passing the exhaust gas through the honeycomb filter.

In a honeycomb filter used for collecting PM in exhaust gas in an exhaust gas purification device, a large number of cells are arranged side by side in the longitudinal direction across a cell wall, and either one end of the cells is sealed. . Therefore, the exhaust gas flowing into one cell always flows out from other cells after passing through the cell wall separating the cells. That is, when such a honeycomb filter is provided in the exhaust gas purification device, PM contained in the exhaust gas is captured by the cell wall when passing through the honeycomb filter. Therefore, the cell wall of the honeycomb filter functions as a filter that purifies the exhaust gas.

In the initial stage when the honeycomb filter collects PM, the PM enters the pores of the cell wall, collects PM inside the cell wall, and closes the pores of the cell wall. become. In the state of depth filtration, PM accumulates inside the cell walls (pores). Therefore, immediately after the start of PM collection, there is a problem that the substantial porosity of the cell wall decreases and the pressure loss increases rapidly.

In Patent Document 1, in order to suppress a sudden pressure increase caused by PM being deeply filtered, the surface of the cell wall constituting the honeycomb structure used as the honeycomb filter has a pore diameter of the cell wall. A honeycomb filter in which a filtration layer having a small pore diameter is formed is disclosed.

International Publication No. 2008/136232

In the conventional honeycomb filter described in Patent Document 1, when the particle size of the particles constituting the filtration layer is large, the interval between the particles is wide, so that the number of PMs passing through the filtration layer increases, and the high collection efficiency. Cannot be obtained.
Moreover, pressure loss will become high because PM which passed the filtration layer carries out depth filtration.

On the other hand, in the conventional honeycomb filter described in Patent Document 1, when the particle diameter of the particles constituting the filtration layer is small, the particles constituting the filtration layer enter the pores of the cell wall and block the pores. Pressure loss becomes high.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a honeycomb filter that suppresses an increase in pressure loss and maintains a high PM collection efficiency.
Another object of the present invention is to provide a method for manufacturing the honeycomb filter.

The honeycomb filter according to claim 1,
A porous honeycomb fired body in which a large number of cells for circulating a fluid are arranged in parallel in the longitudinal direction across a cell wall, and either the fluid inflow side or the fluid outflow side of the cell is sealed. Including a ceramic honeycomb substrate,
A filtration layer composed of at least two layers formed on the surface of the cell wall of the cell having the end on the fluid inflow side opened and the end on the fluid outflow side sealed, and the pores in the cell wall; With
The filtration layer includes a first layer in which particles having a first average particle size are deposited on the surface of the cell wall, and particles having a second average particle size smaller than the first average particle size are And a second layer deposited on the surface of the first layer.

In the honeycomb filter according to the first aspect, the filtration layer composed of at least two layers is formed on the surface of the cell wall and the pores in the cell wall.
The first layer of the filtration layer is formed by depositing particles having a relatively large particle diameter on the surface of the cell wall. Therefore, it can suppress that the particle | grains which comprise a filtration layer permeate into the pore of a cell wall, and block | close the pore. Therefore, an increase in pressure loss can be suppressed.

In the honeycomb filter according to claim 1, the second layer of the filtration layer is formed by depositing particles having a relatively small particle diameter on the surface of the first layer of the filtration layer. Since the second layer has a relatively small pore diameter, PM that is difficult to collect in the first layer having a relatively large pore diameter can be collected in the second layer. As a result, the second layer of the filtration layer can suppress PM from passing through the filtration layer. Therefore, high PM collection efficiency can be maintained.
Further, the second layer of the filtration layer can prevent the PM from being filtered through the filtration layer. As a result, an increase in pressure loss can be suppressed.

As described above, in the honeycomb filter according to the first aspect, the particle diameter of the particles constituting the filtration layer is decreased as the distance from the surface of the cell wall is reduced, thereby suppressing an increase in pressure loss and capturing high PM. Collection efficiency can be maintained.

In the honeycomb filter according to claim 2, the first average particle diameter is 1.2 to 2.5 μm.
When the first average particle diameter is less than 1.2 μm, the particles constituting the first layer easily enter the pores of the cell wall and easily close the pores, so that the pressure loss tends to increase.
On the other hand, when the first average particle diameter exceeds 2.5 μm, the particles constituting the second layer tend to enter the pores formed between the particles of the first layer, so that the pressure loss is likely to increase.

In the honeycomb filter according to claim 3, the second average particle diameter is 0.2 to 1.2 μm.
When the second average particle size is less than 0.2 μm, the particles constituting the second layer easily enter the pores formed between the particles of the first layer and easily close the pores, so the pressure loss increases. It becomes easy to do.
On the other hand, when the second average particle diameter exceeds 1.2 μm, PM tends to pass through the filtration layer, so that it is difficult to obtain sufficient collection efficiency. Moreover, since it becomes easy to carry out depth filtration of PM to a 2nd layer, a pressure loss becomes easy to rise.

5. The honeycomb filter according to claim 4, wherein the ratio of the first average particle diameter to the second average particle diameter is as follows: first average particle diameter: second average particle diameter = 10: 1 to 1. 5: 1.
When the ratio between the first average particle diameter and the second average particle diameter is in the above numerical range, it is possible to prevent the particles constituting the second layer from being filtered through the first layer. Is effectively suppressed, and high PM collection efficiency can be maintained.

In the honeycomb filter according to claim 5, the thickness of the first layer is 5 to 20 μm.
In the honeycomb filter according to claim 6, the thickness of the second layer is 5 to 50 μm.

In the honeycomb filter according to claim 7, the thickness of the filtration layer is 10 to 70 μm.
When the thickness of the filtration layer is less than 10 μm, the PM trapping efficiency is lowered, or the PM is easily filtered through the filtration layer, so that the pressure loss of the honeycomb filter is likely to increase.
On the other hand, when the thickness of the filtration layer exceeds 70 μm, the filtration layer becomes too thick, and the pressure loss tends to increase.
In addition, the thickness of a filtration layer means the thickness of the whole filtration layer containing a 1st layer and a 2nd layer.

In the honeycomb filter according to an eighth aspect, at least one layer constituting the filtration layer is made of a heat-resistant oxide.
In the honeycomb filter according to claim 9, the heat-resistant oxide is at least one selected from the group consisting of alumina, silica, mullite, ceria, zirconia, cordierite, zeolite, and titania.
When the filtration layer is made of a heat-resistant oxide, inconveniences such as melting of the filtration layer do not occur even when regeneration processing for burning PM is performed. Therefore, a honeycomb filter having excellent heat resistance can be obtained.

In the honeycomb filter according to claim 10, at least one layer constituting the filtration layer includes hollow particles.
When the filtration layer is formed of hollow particles, the heat capacity of the filtration layer can be reduced even when the filtration layer is thick.

The honeycomb filter according to claim 11, wherein the filtration layer includes k layers (k is a natural number) stacked on the surface of the second layer, and the n + 2th layer (n Is an average particle diameter of particles deposited on the (n + 1) th layer from the surface of the cell wall.
In the honeycomb filter according to the eleventh aspect, the particle diameter of the particles constituting the filtration layer becomes smaller as the distance from the surface of the cell wall increases. Therefore, an increase in pressure loss can be effectively suppressed and high PM collection efficiency can be maintained.

The method for manufacturing a honeycomb filter according to claim 12,
A method for manufacturing a honeycomb filter according to any one of claims 1 to 11,
Using a ceramic powder, a porous honeycomb fired body in which a large number of cells are arranged in parallel in the longitudinal direction across a cell wall, and either the fluid inflow side or the fluid outflow side of the cell is sealed. A honeycomb fired body manufacturing process to be manufactured;
Including a filtration layer forming step of forming a filtration layer comprising at least two layers on the surface of the cell wall,
The filtration layer forming step includes
A first droplet dispersion step for dispersing a first droplet containing a raw material of the first ceramic particles in a first carrier gas;
A first inflow step of allowing the first carrier gas to flow into a cell having an end on the fluid inflow side opened and a end on the fluid outflow side sealed;
A second droplet dispersion step of dispersing a second droplet having an average particle size smaller than that of the first droplet and containing a raw material of the second ceramic particles in a second carrier gas;
A second inflow step of allowing the second carrier gas to flow into the cell whose end on the fluid inflow side is opened and whose end on the fluid outflow side is sealed after flowing the first carrier gas It is characterized by including.

In the method for manufacturing a honeycomb filter according to a twelfth aspect, the honeycomb filter according to any one of the first to eleventh aspects can be preferably manufactured.
Therefore, it is possible to manufacture a honeycomb filter that suppresses an increase in pressure loss and maintains high PM collection efficiency.

14. The method for manufacturing a honeycomb filter according to claim 13, wherein in the first droplet dispersion step, the first droplet is dispersed in the first carrier gas using a spray, and the second liquid is dispersed. In the droplet dispersion step, the second droplets are dispersed in the second carrier gas using a spray, and the spray pressure in the second droplet dispersion step is the spray pressure in the first droplet dispersion step. Higher than pressure.

Spherical droplets can be produced by dispersing the droplets in a carrier gas using a spray. Since the ceramic particles obtained from the spherical droplets become spherical, the spherical ceramic particles can be deposited on the surface of the cell wall.

Also, the higher the spray pressure, the smaller the droplet size. Therefore, by setting the spray pressure in the second droplet dispersion step to be higher than the spray pressure in the first droplet dispersion step, the particle size of the ceramic particles deposited to form the second layer of the filtration layer is It can be made smaller than the particle diameter of the ceramic particles deposited to form the first layer of the filtration layer.

15. The method for manufacturing a honeycomb filter according to claim 14, wherein at least one of the first droplet and the second droplet is a heat-resistant oxide precursor that becomes a heat-resistant oxide by heating as the raw material. It is included.
When the droplets contain a heat resistant oxide precursor, the heat resistant oxide particles can be obtained by heating the carrier gas. And the filtration layer comprised from the particle | grains of a heat resistant oxide can be formed by flowing the particle | grains of a heat resistant oxide into a cell.
Alternatively, after the droplet containing the heat-resistant oxide precursor is allowed to flow into the cell, the heat-resistant oxide precursor is heated to obtain particles of the heat-resistant oxide. A configured filtration layer can be formed.

The method for manufacturing a honeycomb filter according to claim 15 further includes a first drying step of drying the first carrier gas at 100 to 800 ° C, and in the first inflow step, the first after drying. The carrier gas is allowed to flow into the cell.
Moreover, the manufacturing method of the honeycomb filter according to claim 16 further includes a second drying step of drying the second carrier gas at 100 to 800 ° C., and in the second inflow step, the above-mentioned after drying. A second carrier gas is flowed into the cell.
By heating the carrier gas, for example, a filtration layer composed of heat-resistant oxide particles can be formed as described above.

The method for manufacturing a honeycomb filter according to claim 17, wherein the first heating step of heating the ceramic honeycomb substrate into which the first carrier gas is introduced to 900 to 1500 ° C, and the second carrier gas is used. It further includes at least one step of a second heating step in which the ceramic honeycomb base material that has been introduced is heated to 900 to 1500 ° C.
By heating the ceramic honeycomb substrate into which the carrier gas has been introduced, for example, a filtration layer composed of heat-resistant oxide particles can be formed as described above.

The method for manufacturing a honeycomb filter according to claim 18, wherein the first droplet includes a heat-resistant oxide precursor that becomes a heat-resistant oxide by heating as the raw material. In the drying step, the spherical first ceramic particles are formed from the first droplet.
Furthermore, in the method for manufacturing a honeycomb filter according to claim 19, the second droplet includes a heat-resistant oxide precursor that becomes a heat-resistant oxide by heating as the raw material. In the drying step 2, spherical second ceramic particles are formed from the second droplets.

21. The method for manufacturing a honeycomb filter according to claim 20, wherein in the first inflow step, the first layer is formed by depositing the first ceramic particles on a surface of the cell wall.
Furthermore, in the method for manufacturing a honeycomb filter according to claim 21, in the second inflow step, the second layer is formed by depositing the second ceramic particles on the surface of the first layer. Is done.

FIG. 1 is a perspective view schematically showing an example of the honeycomb filter according to the first embodiment of the present invention. Fig.2 (a) is a perspective view which shows typically an example of the honeycomb fired body which comprises the honeycomb filter shown in FIG. Fig. 2 (b) is a cross-sectional view taken along the line AA of the honeycomb fired body shown in Fig. 2 (a). FIG. 3 is a partially enlarged sectional view of the cell wall of the honeycomb fired body shown in FIGS. 2 (a) and 2 (b). Fig.4 (a) is a schematic diagram for demonstrating the measuring method of the thickness of a 1st layer. FIG. 4B is a schematic diagram for explaining a method for measuring the thickness of the second layer. 5 (a), 5 (b) and 5 (c) are side views schematically showing an example of the cell structure of the honeycomb fired body constituting the honeycomb filter according to the first embodiment of the present invention. . FIG. 6 is a cross-sectional view schematically showing an embodiment of a droplet dispersion step and an inflow step. FIG. 7 is an explanatory diagram of a pressure loss measuring device. FIG. 8 is an explanatory diagram of a collection efficiency measuring device.

Hereinafter, embodiments of the present invention will be specifically described. However, the present invention is not limited to the following embodiments, and can be applied with appropriate modifications without departing from the scope of the present invention.

(First embodiment)
Hereinafter, a first embodiment which is an embodiment of a honeycomb filter and a method for manufacturing a honeycomb filter of the present invention will be described.

First, the honeycomb filter according to the first embodiment of the present invention will be described.
The honeycomb filter according to the first embodiment of the present invention,
A porous honeycomb fired body in which a large number of cells for circulating a fluid are arranged in parallel in the longitudinal direction across a cell wall, and either the fluid inflow side or the fluid outflow side of the cell is sealed. Including a ceramic honeycomb substrate,
A filtration layer composed of at least two layers formed on the surface of the cell wall of the cell having the end on the fluid inflow side opened and the end on the fluid outflow side sealed, and the pores in the cell wall; With
The filtration layer includes a first layer in which particles having a first average particle size are deposited on the surface of the cell wall, and particles having a second average particle size smaller than the first average particle size are And a second layer deposited on the surface of the first layer.

In the honeycomb filter according to the first embodiment of the present invention, the ceramic honeycomb substrate (ceramic block) is composed of a plurality of honeycomb fired bodies. In addition, a large number of cells included in the honeycomb fired body constituting the honeycomb filter are composed of large-capacity cells and small-capacity cells, and the cross-sectional area perpendicular to the longitudinal direction of the large-capacity cells is perpendicular to the longitudinal direction of the small-capacity cells. Larger than the cross-sectional area.

The honeycomb filter according to the first embodiment of the present invention is obtained by forming a filtration layer on the surface of a cell wall of a ceramic honeycomb substrate including a honeycomb fired body.
In the present specification, those having a filtration layer formed on the surface of the cell wall are referred to as “ceramic honeycomb substrate”, and those having the filtration layer formed on the cell wall are referred to as “honeycomb filter”.
Further, in the following description, when the cross section of the honeycomb fired body is simply indicated, it indicates a cross section perpendicular to the longitudinal direction of the honeycomb fired body. Similarly, when simply expressed as the cross-sectional area of the honeycomb fired body, it refers to the area of the cross section perpendicular to the longitudinal direction of the honeycomb fired body.

FIG. 1 is a perspective view schematically showing an example of the honeycomb filter according to the first embodiment of the present invention.
Fig.2 (a) is a perspective view which shows typically an example of the honeycomb fired body which comprises the honeycomb filter shown in FIG. Fig. 2 (b) is a cross-sectional view taken along the line AA of the honeycomb fired body shown in Fig. 2 (a).

In the honeycomb filter 100 shown in FIG. 1, a plurality of honeycomb fired bodies 110 are bound via an adhesive layer 101 to form a ceramic honeycomb substrate (ceramic block) 103, and this ceramic honeycomb substrate (ceramic block) ) On the outer periphery of 103, an outer peripheral coat layer 102 for preventing the leakage of exhaust gas is formed. In addition, the outer periphery coating layer should just be formed as needed.
Such a honeycomb filter formed by binding a plurality of honeycomb fired bodies is also referred to as a collective honeycomb filter.
Although the honeycomb fired body 110 constituting the honeycomb filter 100 will be described later, it is preferably a porous body made of silicon carbide or silicon-containing silicon carbide.

In the honeycomb fired body 110 shown in FIGS. 2 (a) and 2 (b), a large number of cells 111a and 111b are arranged in the longitudinal direction (in the direction of arrow a in FIG. 2 (a)) across the cell wall 113. And an outer peripheral wall 114 is formed on the outer periphery thereof. One end of the cells 111a and 111b is sealed with a sealing material 112a or 112b.
As shown in FIG. 2B, a filtration layer 115 is formed on the surface of the cell wall 113 of the honeycomb fired body 110. In the honeycomb fired body 110 shown in FIG. 2A, the filtration layer 115 is not shown.

In the honeycomb fired body 110 shown in FIGS. 2 (a) and 2 (b), a large-capacity cell 111a whose cross-sectional area perpendicular to the longitudinal direction is relatively larger than the small-capacity cell 111b, and a cross-section perpendicular to the longitudinal direction. Are alternately arranged with small-capacity cells 111b whose area is relatively smaller than that of the large-capacity cell 111a.
The shape of the cross section perpendicular to the longitudinal direction of the large capacity cell 111a is substantially octagonal, and the shape of the cross section perpendicular to the longitudinal direction of the small capacity cell 111b is substantially square.

In the honeycomb fired body 110 shown in FIGS. 2 (a) and 2 (b), the large-capacity cell 111a is opened at the end portion on the first end face 117a side of the honeycomb fired body 110, and on the second end face 117b side. The end is sealed with a sealing material 112a. On the other hand, in the small-capacity cell 111b, the end portion on the second end face 117b side of the honeycomb fired body 110 is opened, and the end portion on the first end face 117a side is sealed with the sealing material 112b.
Therefore, as shown in FIG. 2B, the exhaust gas G ₁ flowing into the large-capacity cell 111a (in FIG. 2B, the exhaust gas is indicated by G ₁ and the flow of the exhaust gas is indicated by an arrow) is always large. After passing through the cell wall 113 separating the capacity cell 111a and the small capacity cell 111b, the small capacity cell 111b flows out. When the exhaust gas _{G 1} is passing through the cell walls 113, since the PM and the like in the exhaust gas is collected, the cell wall 113 that separates the large-volume cells 111a and small-volume cell 111b functions as a filter.
Thus, gas such as exhaust gas can be circulated through the large-capacity cells 111a and the small-capacity cells 111b of the honeycomb fired body 110. When a gas such as exhaust gas is circulated in the direction shown in FIG. 2B, the end of the honeycomb fired body 110 on the first end face 117a side (the end on the side where the small capacity cells 111b are sealed) is fluidized. The end on the inflow side is referred to as the end on the second end face 117b side of the honeycomb fired body 110 (the end on the side where the large-capacity cells 111a are sealed) is referred to as the end on the fluid outflow side.

That is, the large capacity cell 111a having an open end on the fluid inflow side is a cell 111a on the fluid inflow side, and the small capacity cell 111b having an end on the fluid outflow side is a cell on the fluid outflow side. 111b.

Hereinafter, the filtration layer will be described.
FIG. 3 is a partially enlarged sectional view of the cell wall of the honeycomb fired body shown in FIGS. 2 (a) and 2 (b).
As shown in FIG. 3, the filtration layer 115 consists of two layers. Specifically, the filtration layer 115 includes a first layer 115a deposited on the surface of the cell wall 113 and a second layer 115b deposited on the surface of the first layer 115a.
The filtration layer 115 is formed not only on the surface of the cell wall 113 but also on the pores in the cell wall 113.

In the honeycomb filter according to the first embodiment of the present invention, the average particle diameter of the particles constituting the first layer of the filtration layer (hereinafter referred to as the first average particle diameter) is the particles constituting the second layer of the filtration layer. Larger than the average particle diameter (hereinafter referred to as the second average particle diameter). That is, the second average particle size is smaller than the first average particle size.

In the honeycomb filter according to the first embodiment of the present invention, the first average particle diameter is preferably 1.2 to 2.5 μm, more preferably 1.4 to 2.4 μm. More preferably, it is 5-2.3 micrometers.
When the first average particle diameter is less than 1.2 μm, the particles constituting the first layer easily enter the pores of the cell wall and easily close the pores, so that the pressure loss tends to increase.
On the other hand, when the first average particle diameter exceeds 2.5 μm, the particles constituting the second layer tend to enter the pores formed between the particles of the first layer, so that the pressure loss is likely to increase.

In the honeycomb filter according to the first embodiment of the present invention, the second average particle diameter is preferably 0.2 to 1.2 μm, more preferably 0.3 to 1.1 μm, and More preferably, it is 5-1.0 micrometers.
When the second average particle size is less than 0.2 μm, the particles constituting the second layer easily enter the pores formed between the particles of the first layer and easily close the pores, so the pressure loss increases. It becomes easy to do.
On the other hand, when the second average particle diameter exceeds 1.2 μm, PM tends to pass through the filtration layer, so that it is difficult to obtain sufficient collection efficiency. Moreover, since it becomes easy to carry out depth filtration of PM to a 2nd layer, a pressure loss becomes easy to rise.

In addition, a 1st average particle diameter and a 2nd average particle diameter can be measured with the following method.
A honeycomb fired body constituting the honeycomb filter is processed to prepare a sample of 10 mm × 10 mm × 10 mm.
The surface of the sample is observed with a scanning electron microscope (SEM) at any one location of the prepared sample. At this time, the particles constituting the first layer of the filtration layer are set within one field of view. The observation conditions of SEM are acceleration voltage: 15.00 kV, working distance (WD): 15.00 mm, and magnification: 10,000 times.
Next, the particle diameters of all the particles in one field of view are visually measured. The average value of the particle diameters of all particles measured within one field of view is defined as the first average particle diameter.
Similarly, it observes by SEM so that the particle | grains which comprise the 2nd layer of a filtration layer may enter in one visual field, and the particle diameter of all the particles in one visual field is measured visually. The average value of the particle diameters of all particles measured within one field of view is defined as the second average particle diameter.
Note that the boundary between the first layer and the second layer will be described in the method of measuring the thickness of the filtration layer.

In the honeycomb filter according to the first embodiment of the present invention, the ratio of the first average particle diameter to the second average particle diameter is as follows: first average particle diameter: second average particle diameter = 10: 1 to 1 5: 1 is preferable, and 8: 1 to 2: 1 is more preferable.
When the ratio between the first average particle diameter and the second average particle diameter is in the above numerical range, it is possible to prevent the particles constituting the second layer from being filtered through the first layer. Is effectively suppressed, and high PM collection efficiency can be maintained.

In the honeycomb filter according to the first embodiment of the present invention, the filtration layers (the first layer and the second layer) are made of ceramic particles, preferably spherical ceramic particles.
In the honeycomb filter according to the first embodiment of the present invention, at least one of the first layer and the second layer is preferably made of a heat resistant oxide, and both the first layer and the second layer are made of a heat resistant oxide. It is more preferable.
When the filtration layer is made of a heat-resistant oxide, inconveniences such as melting of the filtration layer do not occur even when regeneration processing for burning PM is performed. Therefore, a honeycomb filter having excellent heat resistance can be obtained.
Examples of the heat-resistant oxide include alumina, silica, mullite, ceria, zirconia, cordierite, zeolite, and titania. These may be used alone or in combination of two or more.
Of the above heat-resistant oxides, alumina is preferable.
When both the first layer and the second layer are made of a heat-resistant oxide, the heat-resistant oxide constituting the first layer and the heat-resistant oxide constituting the second layer may be the same type. Although it may be different types, the same type is preferable.

In the honeycomb filter according to the first embodiment of the present invention, the thickness of the first layer is preferably 5 to 20 μm, more preferably 8 to 18 μm, and further preferably 10 to 15 μm.
In the honeycomb filter according to the first embodiment of the present invention, the thickness of the second layer is preferably 5 to 50 μm, more preferably 10 to 40 μm, and further preferably 15 to 35 μm. preferable.

In the honeycomb filter according to the first embodiment of the present invention, the thickness of the filtration layer is preferably 10 to 70 μm, more preferably 18 to 58 μm, and further preferably 25 to 50 μm.
When the thickness of the filtration layer is less than 10 μm, the PM trapping efficiency is lowered, or the PM is easily filtered through the filtration layer, so that the pressure loss of the honeycomb filter is likely to increase.
On the other hand, when the thickness of the filtration layer exceeds 70 μm, the filtration layer becomes too thick, and the pressure loss tends to increase.

In addition, the thickness of a filtration layer can be measured with the following method.
Fig.4 (a) is a schematic diagram for demonstrating the measuring method of the thickness of a 1st layer. FIG. 4B is a schematic diagram for explaining a method for measuring the thickness of the second layer.
First, in the same manner as when measuring the first average particle diameter and the second average particle diameter, the honeycomb fired body constituting the honeycomb filter is processed to produce a 10 mm × 10 mm × 10 mm sample.
The cell cross section is observed with a scanning electron microscope (SEM) at any one location of the prepared sample. The observation conditions of SEM are acceleration voltage: 15.00 kV, working distance (WD): 15.00 mm, and magnification: 500 to 1000 times.
4A and 4B are schematic views instead of actual SEM photographs for easy understanding.
Next, as shown to Fig.4 (a), a line is drawn along the lower surface of the particle | grains which comprise a 1st layer, and this is made into lower surface _LB1 . Further, a line is drawn along the upper surface of the particles constituting the first layer, and this is defined as an upper surface L _S1 .
Subsequently, it is divided into 50 in the left-right direction (longitudinal direction of the honeycomb fired body) in the SEM photograph. At the 50 divided points, the distance between the upper surface L _S1 and the lower surface L _B1 is measured, and is defined as the thickness L ₁ (n) of the first layer at the nth (n is an integer of 1 to 50) point. _Then, the thickness of _{L 1 (1) ~L 1 (} 50) a first layer the average value of.
Similarly, as shown in FIG. 4B, a line is drawn along the lower surface of the particles constituting the second layer, and this is defined as a lower surface _LB2 . Further, a line is drawn along the upper surface of the particles constituting the second layer, and this is defined as an upper surface L _S2 . Incidentally, the lower surface _{L B2} is consistent with the upper surface _{L S1.}
Subsequently, it is divided into 50 in the left-right direction in the SEM photograph. At the 50 divided locations, the distance between the upper surface L _S2 and the lower surface L _B2 is measured and set as the thickness L ₂ (n) of the second layer at the nth location. _Then, the thickness of the L 2 ₍₁₎ ~L 2 the average value of (50) the second layer.
The sum of the thickness of the first layer and the second layer is defined as the thickness of the filtration layer.

In the honeycomb filter according to the first embodiment of the present invention, at least one of the first layer and the second layer may contain hollow particles.

In the honeycomb filter according to the first embodiment of the present invention, the filtration layer is formed on the surface of the cell wall of the cell in which the end portion on the fluid inflow side is opened and the end portion on the fluid outflow side is sealed.
Since the exhaust gas flows into the cell from the fluid inflow side of the honeycomb filter, a large amount of PM in the exhaust gas accumulates on the cell wall of the cell where the end on the fluid inflow side is opened and the end on the fluid outflow side is sealed. Is done. Therefore, when the filtration layer is formed on the surface of the cell wall of the cell where the end on the fluid inflow side is opened and the end on the fluid outflow side is sealed, PM can be collected by the filtration layer. Therefore, depth filtration can be prevented.
In the honeycomb filter according to the first embodiment of the present invention, the filtration layer is formed on the entire surface of the cell wall of the cell in which the end on the fluid inflow side is opened and the end on the fluid outflow side is sealed. However, there may be a portion where the filtration layer is not formed on a part of the surface of the cell wall.

In the honeycomb filter according to the first embodiment of the present invention, examples of the shape of the cross section perpendicular to the longitudinal direction of the large-capacity cell and the small-capacity cell included in the honeycomb fired body include the following shapes.
5 (a), 5 (b) and 5 (c) are side views schematically showing an example of the cell structure of the honeycomb fired body constituting the honeycomb filter according to the first embodiment of the present invention. .
In addition, the filtration layer is not illustrated in FIGS. 5A, 5B, and 5C.

In the honeycomb fired body 120 shown in FIG. 5A, the shape of the cross section perpendicular to the longitudinal direction of the large capacity cell 121a is substantially octagonal, and the shape of the cross section perpendicular to the longitudinal direction of the small capacity cell 121b is substantially rectangular. The large capacity cells 121a and the small capacity cells 121b are alternately arranged. Similarly, in the honeycomb fired body 130 shown in FIG. 5B, the shape of the cross section perpendicular to the longitudinal direction of the large capacity cell 131a is substantially octagonal, and the shape of the cross section perpendicular to the longitudinal direction of the small capacity cell 131b. Is substantially square, and large-capacity cells 131a and small-capacity cells 131b are alternately arranged. The honeycomb fired body 120 shown in FIG. 5 (a) and the honeycomb fired body 130 shown in FIG. 5 (b) have a cross section perpendicular to the longitudinal direction of the large capacity cell with respect to the area of the cross section perpendicular to the longitudinal direction of the small capacity cell. The area ratio of the areas (area of the cross section perpendicular to the longitudinal direction of the large capacity cell / area of the cross section perpendicular to the longitudinal direction of the small capacity cell) is different.
Further, in the honeycomb fired body 140 shown in FIG. 5C, the cross-sectional shape perpendicular to the longitudinal direction of the large-capacity cell 141a is a substantially square shape, and the cross-sectional shape perpendicular to the longitudinal direction of the small-capacity cell 141b is substantially the same. The large-capacity cells 141a and the small-capacity cells 141b are alternately arranged.

In the honeycomb filter according to the first embodiment of the present invention, the area ratio of the area of the cross section perpendicular to the longitudinal direction of the large capacity cell to the area of the cross section perpendicular to the longitudinal direction of the small capacity cell (perpendicular to the longitudinal direction of the large capacity cell) The area of the cross section / the area of the cross section perpendicular to the longitudinal direction of the small-capacity cell) is preferably 1.4 to 2.8, and more preferably 1.5 to 2.4.
By setting the cell on the fluid inflow side as a large capacity cell and the cell on the fluid outflow side as a small capacity cell, a large amount of PM can be deposited on the cell on the fluid inflow side (large capacity cell). Is less than 1.4, the difference between the cross-sectional area of the large-capacity cell and the cross-sectional area of the small-capacity cell is small, and it is difficult to obtain the effect of providing the large-capacity cell and the small-capacity cell. On the other hand, when the area ratio exceeds 2.8, the area of the cross section perpendicular to the longitudinal direction of the small-capacity cell becomes too small, so that gas such as exhaust gas passes through the cell (small-capacity cell) on the fluid outflow side. The pressure loss due to the friction increases.

Next, a method for manufacturing a honeycomb filter according to the first embodiment of the present invention will be described.
The manufacturing method of the honeycomb filter according to the first embodiment of the present invention,
Using a ceramic powder, a porous honeycomb fired body in which a large number of cells are arranged in parallel in the longitudinal direction across a cell wall, and either the fluid inflow side or the fluid outflow side of the cell is sealed. A honeycomb fired body manufacturing process to be manufactured;
Including a filtration layer forming step of forming a filtration layer comprising at least two layers on the surface of the cell wall,
The filtration layer forming step includes
A first droplet dispersion step for dispersing a first droplet containing a raw material of the first ceramic particles in a first carrier gas;
A first inflow step of allowing the first carrier gas to flow into a cell having an end on the fluid inflow side opened and a end on the fluid outflow side sealed;
A second droplet dispersion step of dispersing a second droplet having an average particle size smaller than that of the first droplet and containing a raw material of the second ceramic particles in a second carrier gas;
A second inflow step of allowing the second carrier gas to flow into the cell whose end on the fluid inflow side is opened and whose end on the fluid outflow side is sealed after flowing the first carrier gas It is characterized by including.

In the method for manufacturing a honeycomb filter according to the first embodiment of the present invention, a ceramic honeycomb substrate including a honeycomb fired body is manufactured, and a filtration layer is formed on the surface of the cell wall of the ceramic honeycomb substrate.
Hereinafter, the filtration layer forming step will be described prior to description of other steps.
In the description of this embodiment, the case where the material constituting the filtration layer is a heat-resistant oxide will be described as an example.
In addition, the process for producing the ceramic honeycomb substrate including the honeycomb fired body will be described later.

FIG. 6 is a cross-sectional view schematically showing an embodiment of a droplet dispersion step and an inflow step.
FIG. 6 shows a carrier gas inflow device 1 that is a device for causing a carrier gas to flow into the cells of the ceramic honeycomb substrate.
The carrier gas inflow device 1 includes a droplet dispersion unit 20 that disperses droplets in the carrier gas, a piping unit 30 through which the carrier gas in which the droplets are dispersed passes, and an inflow unit that flows the carrier gas into the cells of the ceramic honeycomb substrate. 40.
Hereinafter, an example in which the first droplet dispersion process and the first inflow process are performed using the carrier gas inflow device 1 will be described.

In the carrier gas inflow device 1, the carrier gas F flows from the lower side to the upper side in FIG. In the carrier gas inflow device 1, the carrier gas F is introduced from below the carrier gas inflow device 1, and is discharged from above the inflow portion 40 through the droplet dispersion portion 20, the piping portion 30, and the inflow portion 40.

The carrier gas F is pressurized from the lower side to the upper side in FIG. 6 by the pressure difference generated by the pressurization from the lower side of the carrier gas inflow device or the suction from the upper side of the carrier gas inflow device. Flows upward in 1.
As the carrier gas, a gas that does not react by heating up to 800 ° C. and does not react with the components in the droplets dispersed in the carrier gas is used.
Examples of the carrier gas include gases such as air, nitrogen, and argon.

In the droplet dispersion unit 20 of the carrier gas inflow device 1, an oxide-containing solution filled in a tank (not shown) is formed into droplets 11 by spraying and dispersed in the carrier gas F.
The oxide-containing solution is a concept including a solution containing a heat-resistant oxide precursor in which a heat-resistant oxide is formed by heating, or a slurry containing heat-resistant oxide particles.

The heat-resistant oxide precursor means a compound derived from a heat-resistant oxide by heating.
Examples thereof include metal hydroxides, carbonates, nitrates, and hydrates constituting the heat-resistant oxide.
Examples of the heat-resistant oxide precursor when the heat-resistant oxide is alumina, that is, the alumina precursor include aluminum nitrate, aluminum hydroxide, boehmite, and diaspore.

The slurry containing heat-resistant oxide particles is a solution in which heat-resistant oxide particles are suspended in water.

The droplets 11 dispersed in the carrier gas F ride on the carrier gas F and flow above the carrier gas inflow device 1 and pass through the piping part 30.

The pipe part 30 of the carrier gas inflow device 1 is a pipe through which the carrier gas F in which the droplets 11 are dispersed passes.
The passage 32 through which the carrier gas F passes in the pipe portion 30 is a space surrounded by the pipe wall 31 of the pipe.

In the carrier gas inflow device 1 used in the present embodiment, a heating mechanism 33 is provided in the piping part 30.
An example of the heating mechanism 33 is an electric heater.

In this embodiment, the pipe wall 31 is heated using the heating mechanism 33, and the carrier gas F in which the droplets 11 are dispersed is allowed to pass through. And it is preferable to heat the carrier gas F which passes the piping part 30, and to heat the droplet 11 disperse | distributed to the carrier gas F. FIG.
When the droplet 11 is heated, the liquid component contained in the droplet evaporates to form spherical ceramic particles 12. In FIG. 6, the spherical ceramic particles 12 are indicated by white circles.
When the heat-resistant oxide precursor is contained in the droplet, the heat-resistant oxide precursor becomes a heat-resistant oxide (spherical ceramic particles) by heating the carrier gas.

In the present embodiment, it is preferable that the pipe wall 31 is heated to 100 to 800 ° C. using the heating mechanism 33 and the carrier gas F in which the droplets 11 are dispersed is allowed to pass for 0.1 to 3.0 seconds.
If the temperature of the heated pipe is less than 100 ° C. and the time for allowing the carrier gas to pass through the pipe is less than 0.1 seconds, it becomes difficult to sufficiently evaporate the water in the droplets. On the other hand, if the temperature of the heated pipe exceeds 800 ° C. and the time for passing the carrier gas through the pipe exceeds 3.0 seconds, the energy required for manufacturing the honeycomb filter becomes too large. The manufacturing efficiency of the honeycomb filter is reduced.

In the present embodiment, the length of the pipe is not particularly limited, but is preferably 500 to 3000 mm.
If the length of the pipe is less than 500 mm, it becomes difficult to sufficiently evaporate the water in the droplets even if the speed of passing the carrier gas through the pipe is slowed. On the other hand, if the length of the pipe exceeds 3000 mm, the apparatus for manufacturing the honeycomb filter becomes too large, and the manufacturing efficiency of the honeycomb filter is lowered.

While being dispersed in the carrier gas F, the spherical ceramic particles 12 ride on the flow of the carrier gas F and flow above the carrier gas inflow device 1, and flow into the cells of the ceramic honeycomb substrate 103 at the inflow portion 40.

In the present embodiment, a ceramic block in which a plurality of honeycomb fired bodies are bound through an adhesive layer is used as the ceramic honeycomb substrate.
The ceramic honeycomb substrate 103 is arranged at the upper part of the carrier gas inflow device 1 so as to close the outlet of the carrier gas inflow device 1.
Therefore, the carrier gas F always flows into the ceramic honeycomb substrate 103.

FIG. 6 schematically shows a cross section of the honeycomb fired body constituting the ceramic block (a cross section similar to that shown in FIG. 2B) as a cross section of the ceramic honeycomb substrate 103.
In the ceramic honeycomb substrate 103, the end portion of the cell 111a on the fluid inflow side is open, and the cell 111b on the fluid outflow side is sealed.
Therefore, the carrier gas F flows into the ceramic honeycomb substrate 103 from the opening of the cell 111a on the fluid inflow side.
When the carrier gas F in which the spherical ceramic particles 12 are dispersed flows into the cell 111 a on the fluid inflow side of the ceramic honeycomb substrate 103, the spherical ceramic particles 12 are deposited on the surface of the cell wall 113 of the ceramic honeycomb substrate 103.

And in this embodiment, it is preferable to heat the ceramic honeycomb base material 103 to 100-800 degreeC, and to make carrier gas F flow in into the heated cell.
When the ceramic honeycomb substrate 103 is heated to 100 to 800 ° C., even if the liquid component remains in the spherical ceramic particles 12, the liquid component evaporates, and the surface of the cell wall in a dry powder state. To deposit.

The carrier gas F flows into the inside of the ceramic honeycomb substrate 103 from the opening of the cell 111a on the fluid inflow side, passes through the cell wall 113 of the ceramic honeycomb substrate 103, and flows out from the opening of the cell 111b on the fluid outflow side.
The first inflow process is performed by such a procedure.
Through the first inflow process, spherical ceramic particles can be deposited on the surface of the cell wall.

Subsequently, it is preferable to perform a heating process of the ceramic honeycomb substrate.
It is preferable to heat the ceramic honeycomb base material in which the spherical ceramic particles are adhered to the cell walls through the carrier gas inflow process at a furnace temperature of 900 to 1500 ° C. using a heating furnace.
The heating atmosphere is preferably an air atmosphere, a nitrogen atmosphere, or an argon atmosphere.

And the spherical ceramic particles adhering to the surface of the cell wall cause heat shrinkage by heat sintering and firmly adhere to the surface of the cell wall.

Through the above steps, the first layer of the filtration layer can be formed on the surface of the cell wall.
The step of heating the carrier gas (also referred to as the first drying step), the step of flowing the carrier gas while heating the ceramic honeycomb substrate, and the step of heating the ceramic honeycomb substrate after flowing the carrier gas Regarding (also referred to as the first heating step), it is not always necessary to perform all the steps, and at least one step may be performed.
Among these, it is preferable to perform the first drying step and the first heating step.

Thereafter, a second droplet dispersion step and a second inflow step are performed.
In the second droplet dispersion step, droplets having an average particle diameter different from that in the first droplet dispersion step are used. Specifically, the average particle size of the droplets in the second droplet dispersion step is made smaller than the average particle size of the droplets in the first droplet dispersion step.
Except for the above points, the second droplet dispersing step is the same as the first droplet dispersing step.
The second inflow process is the same as the first inflow process described above.
Through the second inflow process, spherical ceramic particles can be deposited on the surface of the first layer.

The method for reducing the average particle size of the droplets in the second droplet dispersing step to be smaller than the average particle size of the droplets in the first droplet dispersing step is not particularly limited, but the second droplet dispersing step It is preferable that the spray pressure in the is higher than the spray pressure in the first droplet dispersion step.
The higher the spray pressure, the smaller the droplet size can be made. Therefore, by setting the spray pressure in the second droplet dispersion step higher than the spray pressure in the first droplet dispersion step, the particle size of the spherical ceramic particles deposited to form the second layer of the filtration layer can be reduced. The particle diameter of the spherical ceramic particles deposited to form the first layer of the filtration layer can be made smaller.

Through the above steps, the second layer of the filtration layer can be formed on the surface of the first layer of the filtration layer.
As in forming the first layer of the filtration layer, a step of heating the carrier gas (also referred to as a second drying step), a step of flowing the carrier gas while heating the ceramic honeycomb substrate, and a carrier You may perform the process (it is also called a 2nd heating process) of heating a ceramic honeycomb base material, after flowing in gas. However, it is not always necessary to perform all the steps, and at least one step may be performed.
Among these, it is preferable to perform a 2nd drying process and a 2nd heating process.

Hereinafter, a process for producing a ceramic honeycomb substrate including a honeycomb fired body in the method for manufacturing a honeycomb filter according to the first embodiment of the present invention will be described.
The ceramic honeycomb substrate produced below is a ceramic block in which a plurality of honeycomb fired bodies are bundled through an adhesive layer.
The case where silicon carbide is used as the ceramic powder will be described.
(1) A forming step for producing a honeycomb formed body by extruding a wet mixture containing a ceramic powder and a binder is performed.
Specifically, first, a wet mixture for manufacturing a honeycomb formed body is prepared by mixing silicon carbide powder having different average particle sizes as ceramic powder, an organic binder, a liquid plasticizer, a lubricant, and water. To prepare.
Subsequently, the wet mixture is put into an extruder and extruded to produce a honeycomb formed body having a predetermined shape.
At this time, a honeycomb formed body is manufactured using a mold that has a cross-sectional shape having a cell structure (cell shape and cell arrangement) shown in FIGS. 2 (a) and 2 (b).

(2) The honeycomb formed body is cut to a predetermined length, dried using a microwave dryer, hot air dryer, dielectric dryer, vacuum dryer, vacuum dryer, freeze dryer, etc. A sealing step of filling the cell with a sealing material paste as a sealing material and sealing the cell is performed.
Here, the wet mixture can be used as the sealing material paste.

(3) After heating the honeycomb formed body in a degreasing furnace and performing a degreasing step of removing organic substances in the honeycomb formed body, the degreased honeycomb formed body is conveyed to a firing furnace, and the firing step is performed. A honeycomb fired body as shown in FIGS. 2A and 2B is manufactured.
In addition, the sealing material paste with which the edge part of the cell was filled is baked by heating and becomes a sealing material.
Moreover, the conditions currently used when manufacturing a honeycomb fired body can be applied to the conditions of a cutting process, a drying process, a sealing process, a degreasing process, and a firing process.

(4) A bundling process is performed in which a plurality of honeycomb fired bodies are sequentially stacked and bonded via an adhesive paste on a support base to produce a honeycomb aggregate in which a plurality of honeycomb fired bodies are stacked.
As the adhesive paste, for example, a paste made of an inorganic binder, an organic binder, and inorganic particles is used. The adhesive paste may further contain inorganic fibers and / or whiskers.

(5) The honeycomb aggregate is heated and the adhesive paste is heated and solidified to form an adhesive layer, thereby producing a quadrangular columnar ceramic block.
As the conditions for heating and solidifying the adhesive paste, the conditions conventionally used when producing a honeycomb filter can be applied.

(6) A cutting process for cutting the ceramic block is performed.
Specifically, a ceramic block whose outer periphery is processed into a substantially cylindrical shape is manufactured by cutting the outer periphery of the ceramic block using a diamond cutter.

(7) An outer peripheral coating layer forming step is performed in which an outer peripheral coating material paste is applied to the outer peripheral surface of the substantially cylindrical ceramic block, and dried and solidified to form an outer peripheral coating layer.
Here, the said adhesive paste can be used as an outer periphery coating material paste. In addition, you may use the paste of a composition different from the said adhesive paste as an outer periphery coating material paste.
Note that the outer peripheral coat layer is not necessarily provided, and may be provided as necessary.
By providing the outer peripheral coating layer, the shape of the outer periphery of the ceramic block can be adjusted to obtain a cylindrical ceramic honeycomb substrate.
Through the above steps, a ceramic honeycomb substrate including a honeycomb fired body can be manufactured.

And the honeycomb filter which concerns on 1st embodiment of this invention is producible by performing the filtration layer formation process mentioned above with respect to the ceramic honeycomb base material.

Hereinafter, effects of the honeycomb filter and the method for manufacturing the honeycomb filter according to the first embodiment of the present invention will be listed.
(1) In the honeycomb filter of the present embodiment, two filtration layers are formed on the surface of the cell wall and the pores in the cell wall.
The first layer of the filtration layer is formed by depositing particles having a relatively large particle diameter on the surface of the cell wall. Therefore, it can suppress that the particle | grains which comprise a filtration layer permeate into the pore of a cell wall, and block | close the pore. Therefore, an increase in pressure loss can be suppressed.

(2) In the honeycomb filter of the present embodiment, the second layer of the filtration layer is formed by depositing particles having a relatively small particle diameter on the surface of the first layer of the filtration layer. Since the second layer has a relatively small pore diameter, PM that is difficult to collect in the first layer having a relatively large pore diameter can be collected in the second layer. As a result, the second layer of the filtration layer can suppress PM from passing through the filtration layer. Therefore, high PM collection efficiency can be maintained.
Further, the second layer of the filtration layer can prevent the PM from being filtered through the filtration layer. As a result, an increase in pressure loss can be suppressed.

(3) In the honeycomb filter of the present embodiment, the particle diameter of the particles constituting the filtration layer is reduced as the distance from the surface of the cell wall decreases, thereby suppressing an increase in pressure loss and maintaining high PM collection efficiency. can do.

(4) In the method for manufacturing a honeycomb filter of the present embodiment, the honeycomb filter of the present embodiment can be preferably manufactured.
Therefore, it is possible to manufacture a honeycomb filter that suppresses an increase in pressure loss and maintains high PM collection efficiency.

(Example)
Examples of the honeycomb filter and the method for manufacturing the honeycomb filter according to the first embodiment of the present invention will be described below more specifically. In addition, this invention is not limited only to these Examples.

Example 1
(Production of ceramic honeycomb substrate)
First, 54.6% by weight of a coarse powder of silicon carbide having an average particle diameter of 22 μm and 23.4% by weight of a fine powder of silicon carbide having an average particle diameter of 0.5 μm were mixed. An organic binder (methylcellulose) 4.3 wt%, a lubricant (Unilube made by NOF Corporation) 2.6 wt%, glycerin 1.2 wt%, and water 13.9 wt% are added and kneaded to obtain a wet mixture. After being obtained, a molding step of extrusion molding was performed.
In this step, a raw honeycomb molded body having the same shape as the honeycomb fired body 110 shown in FIG. 2A and having no cell plugged was produced.

Subsequently, the raw honeycomb formed body was dried using a microwave dryer, thereby manufacturing a dried body of the honeycomb formed body. Then, the sealing material paste was filled in predetermined cells of the dried honeycomb molded body to seal the cells. The wet mixture was used as a sealing material paste. After sealing the cells, the dried honeycomb molded body filled with the plug paste was again dried using a dryer.

Subsequently, a degreasing treatment for degreasing the dried honeycomb molded body after cell sealing at 400 ° C. was performed, and further a firing treatment was performed under conditions of 2200 ° C. and 3 hours in an atmospheric argon atmosphere.
Thereby, a square pillar honeycomb fired body was produced.
The manufactured honeycomb fired body has a height of 34.3 mm × a width of 34.3 mm × a length of 150 mm, an average pore diameter of 24 μm, a porosity of 64%, and the number of cells (cell density) of 54.2 cells / cm ² ( 350 cells / inch ² ) and the cell wall thickness was 0.28 mm (11 mil).

By applying an adhesive paste between the honeycomb fired bodies obtained by the above process to form an adhesive paste layer, and heating and solidifying the adhesive paste layer to form an adhesive layer, 16 honeycomb fired bodies are obtained. A substantially prismatic ceramic block formed by binding through an adhesive layer was produced.
As the adhesive paste, 30% by weight of alumina fibers having an average fiber length of 20 μm, 21% by weight of silicon carbide particles having an average particle diameter of 0.6 μm, 15% by weight of silica sol, 5.6% by weight of carboxymethylcellulose, and water 28 An adhesive paste containing 4% by weight was used.

Thereafter, a cylindrical ceramic block having a diameter of 142 mm was prepared by cutting the outer periphery of the prismatic ceramic block using a diamond cutter.

Next, the outer periphery coating material paste was applied to the outer peripheral surface of the cylindrical ceramic block, and the outer periphery coating material paste was heated and solidified at 120 ° C. to form an outer periphery coating layer on the outer periphery of the ceramic block.
In addition, as the said outer periphery coating material paste, the paste similar to the said adhesive material paste was used.
Through the above steps, a cylindrical ceramic honeycomb substrate having a diameter of 143.8 mm and a length of 150 mm was produced.

(Filtration layer forming step)
A filter layer was formed on the ceramic honeycomb substrate using the carrier gas inflow device shown in FIG.
As shown in FIG. 6, a ceramic honeycomb substrate was disposed above the carrier gas inflow device.
At this time, the ceramic honeycomb substrate was disposed with the opening of a large-capacity cell as a cell on the fluid inflow side facing downward of the carrier gas inflow device.

[First droplet dispersion step]
As the oxide-containing solution, a solution containing boehmite which is a heat-resistant oxide precursor was prepared. The concentration of boehmite was 3.8 mol / L (solid content concentration: 20% by weight).
Then, the droplets containing boehmite were dispersed in the carrier gas by spraying. The spray pressure was 100 kPa.

[First inflow process]
The temperature of the wall of the pipe of the carrier gas inflow device is heated to 200 ° C., and the carrier gas is flowed toward the upper side of the carrier gas inflow device (ceramic honeycomb substrate side) at a flow rate of 1.8 mm / sec. The water in the droplets dispersed therein was evaporated. When the carrier gas passed through the pipe, the water in the droplets evaporated, and the droplets became spherical alumina particles.
The length of the pipe was 1200 mm.

The carrier gas in which the spherical alumina particles were dispersed was allowed to flow into the cells of the ceramic honeycomb substrate, and 5 g / L of spherical alumina particles were adhered to the surface of the cell walls.
Thereafter, the ceramic honeycomb substrate was taken out from the carrier gas inflow device and heated in a firing furnace at 1350 ° C. for 3 hours in an air atmosphere.
Through the above process, the first layer of the filtration layer was formed on the surface of the cell wall.

[Second droplet dispersion step and second inflow step]
Thereafter, the same steps as the first droplet dispersion step and the first inflow step were performed except that the spray pressure was changed to 330 kPa and the flow rate of the carrier gas was changed to 7.0 mm / sec.
By the above process, the second layer of the filtration layer was formed on the surface of the first layer of the filtration layer.

The honeycomb filter of Example 1 was manufactured through the above process. In the honeycomb filter of Example 1, two filtration layers made of alumina particles are formed on the surface of the cell wall.

(Example 2 to Example 4)
A honeycomb filter was manufactured in the same manner as in Example 1 except that the spray pressure and the flow rate of the carrier gas were changed to the values shown in Table 1.

(Comparative Example 1)
First, in the same manner as in Example 1, a ceramic honeycomb substrate was prepared, and the first droplet dispersion step and the first inflow step were performed. In Comparative Example 1, 15 g / L spherical alumina particles were adhered to the surface of the cell wall. Through the above process, the first layer of the filtration layer was formed on the surface of the cell wall.
In Comparative Example 1, the second droplet dispersion step and the second inflow step were not performed. That is, the second layer of the filtration layer was not formed.
The honeycomb filter of Comparative Example 1 was manufactured by the above process. In the honeycomb filter of Comparative Example 1, one filtration layer made of alumina particles is formed on the surface of the cell wall.

The honeycomb filter manufactured in Examples 1 to 4 and Comparative Example 1 was evaluated as follows.

(Measurement of average particle diameter and filter layer thickness)
For each honeycomb filter, the first average particle diameter, the second average particle diameter, the thickness of the first layer, and the thickness of the second layer were measured according to the method described above.
As SEM, Hitachi FE-SEM S-4800 was used.
The results are shown in Table 2.

From Table 2, in the honeycomb filter manufactured in Examples 1 to 4, it was confirmed that a filtration layer composed of two layers was formed. Specifically, the filtration layer includes a first layer in which particles having a first average particle size are deposited on the surface of the cell wall, and particles having a second average particle size smaller than the first average particle size. Was made up of a second layer deposited on the first layer.
On the other hand, in the honeycomb filter manufactured in Comparative Example 1, it was confirmed that a single filtration layer was formed.

(Measurement of pressure loss)
Pressure loss was measured using a pressure loss measuring apparatus 510 as shown in FIG.
FIG. 7 is an explanatory diagram of a pressure loss measuring device.
This pressure loss measuring device 510 can detect the pressure before and after the honeycomb filter 100 by disposing the honeycomb filter 100 in the metal casing 513 in the exhaust gas pipe 512 of a 1.6 L (liter) diesel engine 511. A pressure gauge 514 is attached so that
The engine 511 was operated at a torque of 50 Nm and a rotation speed of 3000 rpm, and the differential pressure in a state where PM was not deposited on the honeycomb filter 100, that is, the initial pressure loss was measured.
The obtained measurement results are shown in Table 3.

(Measurement of collection efficiency)
The collection efficiency of PM was measured using a collection efficiency measuring device 530 as shown in FIG. FIG. 8 is an explanatory diagram of a collection efficiency measuring device.
The collection efficiency measuring device 530 includes a 1.6 L (liter) diesel engine 531, an exhaust gas pipe 532 that distributes exhaust gas from the engine 531, and a honeycomb filter 100 that is connected to the exhaust gas pipe 532 and wound with an alumina mat 533. The metal casing 534 to be fixed, the sampler 535 that samples the exhaust gas before flowing through the honeycomb filter 100, the sampler 536 that samples the exhaust gas after flowing through the honeycomb filter 100, and the exhaust gas sampled by the samplers 535 and 536 is diluted. Scanning mobility particle size analyzer (Scanning Mobility P) equipped with a diluter 537 and a PM counter 538 (manufactured by TSI, agglomerated particle counter 3022A-S) for measuring the amount of PM contained in the diluted exhaust gas rticle Sizer SMPS) is configured as.

Next, the measurement procedure will be described. The engine 531 was operated at a torque of 50 Nm and a rotation speed of 3000 rpm, and the exhaust gas from the engine 531 was passed through the honeycomb filter 100. At this time, the PM amount P ₀ before passing through the honeycomb filter 100 and the PM amount P ₁ after passing through the honeycomb filter 100 were grasped using the PM counter 538. And the collection efficiency was computed using the following formula.
Collection efficiency (%) = [(P ₀ −P ₁ ) / P ₀ ] × 100
The collection efficiency was measured after collecting 0.1 g of PM per liter of honeycomb filter volume.
The obtained measurement results are shown in Table 3.

From Table 3, it was found that the initial pressure loss was lower in the honeycomb filters of Examples 1 to 4 than in the honeycomb filter of Comparative Example 1.
Therefore, the initial pressure loss can be reduced by forming a filtration layer comprising a first layer having a relatively large particle diameter and a second layer having a relatively small particle diameter.

Table 3 also revealed that the honeycomb filters of Examples 1 to 4 had a high collection efficiency of 98.5%.
On the other hand, in the honeycomb filter of Comparative Example 1, the collection efficiency was as high as 98.0%. However, as described above, the honeycomb filter of Comparative Example 1 is inferior to the honeycomb filters of Examples 1 to 4 in terms of initial pressure loss.

From the above, in the honeycomb filters of Examples 1 to 4, it is possible to suppress an increase in pressure loss and maintain high PM collection efficiency.

(Other embodiments)
In the honeycomb filter according to the first embodiment of the present invention, the case where the filtration layer is composed of two layers has been described.
However, in the honeycomb filter according to another embodiment of the present invention, the filtration layer includes a first layer in which particles having a first average particle size are deposited on the surface of the cell wall, and the first average particle size. As long as the particles having a small second average particle diameter include the second layer deposited on the first layer, the configuration is not limited to the two-layer configuration.
That is, the filtration layer may include k layers (k is a natural number) stacked on the surface of the second layer. In this case, the average particle diameter of particles deposited in the (n + 2) th layer (n is a natural number of 1 or more and k or less) from the cell wall surface is the particles deposited in the (n + 1) th layer from the cell wall surface. It is sufficient that the average particle diameter is smaller than the average particle diameter.
Also for such a honeycomb filter, the average particle diameter of particles deposited in each layer can be measured by the method described above.
Also in the above honeycomb filter, the particle diameter of the particles constituting the filtration layer becomes smaller as the distance from the surface of the cell wall increases. Therefore, an increase in pressure loss can be effectively suppressed and high PM collection efficiency can be maintained.

In the honeycomb filter according to the embodiment of the present invention, when the filtration layer includes two or more layers, the thickness of the filtration layer is preferably 10 to 70 μm.
As described above, the thickness of the filtration layer refers to the thickness of the entire filtration layer including the first layer and the second layer.

In the honeycomb filter according to the first embodiment of the present invention, the filtration layer is formed only on the surface of the cell wall of the cell in which the end portion on the fluid inflow side is opened and the end portion on the fluid outflow side is sealed. .
However, in the honeycomb filter according to another embodiment of the present invention, the filtration layer has an opening at the end on the fluid inflow side and a surface of the cell wall of the cell where the end on the fluid outflow side is sealed, The end portion on the fluid inflow side may be sealed, and the end portion on the fluid outflow side may be formed on the surface of the cell wall of the cell.
Such a honeycomb filter can be manufactured by immersing the ceramic honeycomb substrate in a slurry containing spherical ceramic particles prepared in advance and then heating.

In the method for manufacturing a honeycomb filter according to the first embodiment of the present invention, a heat-resistant oxide precursor that becomes a heat-resistant oxide by heating is contained as a raw material in both the first droplet and the second droplet. I have explained the case.
However, in the method for manufacturing a honeycomb filter according to the embodiment of the present invention, it is sufficient that at least one of the first droplet and the second droplet includes a heat-resistant oxide precursor as a raw material.
When the droplets contain a heat resistant oxide precursor, the heat resistant oxide particles can be obtained by heating the carrier gas. And the filtration layer comprised from the particle | grains of a heat resistant oxide can be formed by flowing the particle | grains of a heat resistant oxide into a cell.
Alternatively, after the droplet containing the heat-resistant oxide precursor is allowed to flow into the cell, the heat-resistant oxide precursor is heated to obtain particles of the heat-resistant oxide. A configured filtration layer can be formed.

In the method for manufacturing a honeycomb filter according to the embodiment of the present invention, at least one of the first droplet and the second droplet may include heat-resistant oxide particles as a raw material.
When the heat-resistant oxide particles are contained in the droplets, the moisture in the droplets can be removed by heating the carrier gas to obtain heat-resistant oxide particles. And the filtration layer comprised from the particle | grains of a heat resistant oxide can be formed by flowing the particle | grains of a heat resistant oxide into a cell.
Moreover, the filtration layer comprised of the particles of the heat-resistant oxide can also be formed by removing the moisture in the droplets after flowing the droplet containing the heat-resistant oxide particles into the cell.

In the honeycomb filter according to the embodiment of the present invention, the shape of the cross section perpendicular to the longitudinal direction of the cells of the honeycomb fired body constituting the honeycomb filter may be all equal, or at one end face of the honeycomb fired body. The cross-sectional areas perpendicular to the longitudinal direction of the sealed cell and the opened cell may be equal to each other.

In the honeycomb filter according to the embodiment of the present invention, the ceramic honeycomb substrate (ceramic block) may be composed of one honeycomb fired body.
Such a honeycomb filter made of one honeycomb fired body is also referred to as an integral honeycomb filter. As the main constituent material of the integral honeycomb filter, cordierite or aluminum titanate can be used.

In the honeycomb filter according to the embodiment of the present invention, the shape of the cross section perpendicular to the longitudinal direction of the honeycomb fired body of each cell of the honeycomb fired body is not limited to a substantially square shape. Any shape such as a substantially pentagon, a substantially hexagon, a substantially trapezoid, or a substantially octagon may be used. Various shapes may be mixed.

The porosity of the honeycomb fired body constituting the honeycomb filter according to the embodiment of the present invention is not particularly limited, but is preferably 35 to 70%.
When the porosity of the honeycomb fired body is less than 35%, the honeycomb fired body is likely to be clogged. On the other hand, when the porosity of the honeycomb fired body exceeds 70%, the strength of the honeycomb fired body is lowered and easily broken.

The average pore diameter of the honeycomb fired body constituting the honeycomb filter according to the embodiment of the present invention is preferably 5 to 30 μm.
When the average pore diameter of the honeycomb fired body is less than 5 μm, the honeycomb fired body is easily clogged. On the other hand, when the average pore diameter of the honeycomb fired body exceeds 30 μm, the particulates pass through the pores of the cell wall, the honeycomb fired body cannot collect the particulates, and the honeycomb filter functions as a filter. I can't.

The porosity and pore diameter can be measured by a conventionally known mercury intrusion method.

In the honeycomb filter of the present invention, a filtration layer comprising at least two layers is formed on the surface of the cell wall of the ceramic honeycomb substrate, and the filtration layer contains particles having a first average particle diameter. A first layer deposited on the surface of the first layer and a second layer in which particles having a second average particle size smaller than the first average particle size are deposited on the surface of the first layer. As a component.
The essential components include various configurations described in detail in the first embodiment and the other embodiments (for example, the configuration of the filtration layer, the method of forming the filtration layer, the cell structure of the honeycomb fired body, the manufacture of the honeycomb filter) Desired effects can be obtained by appropriately combining the steps and the like.

DESCRIPTION OF SYMBOLS 1 Carrier gas inflow apparatus 11 Droplet 12 Spherical ceramic particle 100 Honeycomb filter 103 Ceramic honeycomb base material (ceramic block)
110, 120, 130, 140 Honeycomb fired bodies 111a, 111b, 121a, 121b, 131a, 131b, 141a, 141b Cell 113 Cell wall 115 Filtration layer 115a First layer (first layer of filtration layer)
115b 2nd layer (2nd layer of filtration layer)
F Carrier gas G ₁ Exhaust gas

Claims (21)

A porous honeycomb fired body in which a large number of cells for circulating a fluid are arranged in parallel in the longitudinal direction across a cell wall, and either the fluid inflow side or the fluid outflow side of the cell is sealed. Including a ceramic honeycomb substrate,
A filtration layer composed of at least two layers formed on the surface of the cell wall of the cell whose end on the fluid inflow side is open and whose end on the fluid outflow side is sealed and the pores in the cell wall; With
The filtration layer includes a first layer in which particles having a first average particle size are deposited on a surface of the cell wall, and particles having a second average particle size smaller than the first average particle size. A honeycomb filter comprising: a second layer deposited on a surface of the first layer. The honeycomb filter according to claim 1, wherein the first average particle diameter is 1.2 to 2.5 µm. The honeycomb filter according to claim 1 or 2, wherein the second average particle diameter is 0.2 to 1.2 µm. The ratio between the first average particle size and the second average particle size is as follows: first average particle size: second average particle size = 10: 1 to 1.5: 1 The honeycomb filter according to any one of the above. The honeycomb filter according to any one of claims 1 to 4, wherein the first layer has a thickness of 5 to 20 µm. The honeycomb filter according to any one of claims 1 to 5, wherein the thickness of the second layer is 5 to 50 µm. The honeycomb filter according to any one of claims 1 to 6, wherein the filtration layer has a thickness of 10 to 70 µm. The honeycomb filter according to any one of claims 1 to 7, wherein at least one layer constituting the filtration layer is made of a heat-resistant oxide. The honeycomb filter according to claim 8, wherein the heat-resistant oxide is at least one selected from the group consisting of alumina, silica, mullite, ceria, zirconia, cordierite, zeolite, and titania. The honeycomb filter according to any one of claims 1 to 9, wherein at least one layer constituting the filtration layer includes hollow particles. The filtration layer includes k layers (k is a natural number) stacked on the surface of the second layer,
The average particle diameter of the particles deposited in the n + 2th layer (n is a natural number of 1 or more and k or less) from the cell wall surface is the average particle diameter of the particles deposited in the (n + 1) th layer from the cell wall surface. The honeycomb filter according to any one of claims 1 to 10, wherein the honeycomb filter is smaller than the diameter. A method for manufacturing a honeycomb filter according to any one of claims 1 to 11,
Using a ceramic powder, a porous honeycomb fired body in which a large number of cells are juxtaposed in the longitudinal direction across a cell wall, and either the fluid inflow side or the fluid outflow side of the cell is sealed. A honeycomb fired body manufacturing process to be manufactured;
Forming a filtration layer comprising at least two layers on the surface of the cell wall; and
The filtration layer forming step includes
A first droplet dispersion step for dispersing a first droplet containing a raw material of the first ceramic particles in a first carrier gas;
A first inflow step of allowing the first carrier gas to flow into a cell having an end on the fluid inflow side opened and a end on the fluid outflow side sealed;
A second droplet dispersion step of dispersing a second droplet having an average particle size smaller than that of the first droplet and containing a raw material of the second ceramic particles in a second carrier gas;
A second inflow step of allowing the second carrier gas to flow into a cell having an open end on the fluid inflow side and a sealed end on the fluid outflow side after flowing the first carrier gas A method for manufacturing a honeycomb filter, comprising: In the first droplet dispersion step, the first droplet is dispersed in the first carrier gas using a spray,
In the second droplet dispersion step, the second droplet is dispersed in the second carrier gas using a spray,
The method for manufacturing a honeycomb filter according to claim 12, wherein a spray pressure in the second droplet dispersion step is higher than a spray pressure in the first droplet dispersion step. The heat-resistant oxide precursor which becomes a heat-resistant oxide by heating is contained in at least one of the first droplet and the second droplet as the raw material. Manufacturing method of honeycomb filter. A first drying step of drying the first carrier gas at 100 to 800 ° C .;
The method for manufacturing a honeycomb filter according to any one of claims 12 to 14, wherein in the first inflow step, the dried first carrier gas is caused to flow into the cell. A second drying step of drying the second carrier gas at 100 to 800 ° C .;
The method for manufacturing a honeycomb filter according to any one of claims 12 to 15, wherein in the second inflow step, the second carrier gas after drying is caused to flow into the cell. A first heating step of heating the ceramic honeycomb substrate into which the first carrier gas has been introduced to 900 to 1500 ° C, and a ceramic honeycomb substrate into which the second carrier gas has been introduced to 900 to 1500 ° C The method for manufacturing a honeycomb filter according to any one of claims 12 to 16, further comprising at least one step of a second heating step of heating. The first droplet contains a heat-resistant oxide precursor that becomes a heat-resistant oxide by heating as the raw material,
The method for manufacturing a honeycomb filter according to claim 15, wherein, in the first drying step, the first ceramic particles having a spherical shape are formed from the first droplets. The second droplet contains a heat-resistant oxide precursor that becomes a heat-resistant oxide by heating as the raw material,
The method for manufacturing a honeycomb filter according to claim 16, wherein, in the second drying step, spherical second ceramic particles are formed from the second droplet. The honeycomb filter according to any one of claims 12 to 19, wherein, in the first inflow step, the first layer is formed by depositing the first ceramic particles on a surface of the cell wall. Method. 21. The honeycomb filter according to any one of claims 12 to 20, wherein, in the second inflow step, the second layer is formed by depositing the second ceramic particles on a surface of the first layer. Manufacturing method.

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